Eren's mistake
by sweetandsnowy
Summary: Eren want's Levi as a mate and has been using Armin for the past year to make Levi jealous. Armin finds out Eren's having a relationship with Levi and decides not to tell Eren he's pregnant and leaves the Survery corps. Slash,yaoi,mpreg. Main Pairings:/Eren x Armin / Jean x Marco / Levi x Erwin/.


**Copyright / Disclaimer: I do not own AOT,the oc's mine.  
**

**Warnings:Mentions of sex,language,slash,yaoi,mpreg, and Alpha,Beta and Omega dynamics.**

**Authors Note:I really like the Alpha,Beta, and Omega AU so I decided that it was going to be used for my first Eremin fanfic.  
**

**Pairings: Major Pairings: Eremin (Eren x Armin) Eruri (Levi x Erwin) Jeanmarco (Jean x Marco).**

**Minor pairings: Ereri (Eren x Levi) (Reiner x Armin).**

* * *

"Hey Armin can you give this to Captain Levi"Asked Jean handing Armin a folder absent mindedly.

"Sure where is he"Agreed Armin testing the weight of the folder.

"He's in his room"Said Jean gesturing to the hallway that lead to Levi's bedroom.

Armin nodded before heading down the hallway a odd feeling of dread washing over him,he frowned mentally shaking off the feeling before getting back to the task at hand.

As he neared Levi's bedroom he heard noises,Armin's nose scrunched up in confusion.

'Captain Levi is usually more quiet' He thought a frown marring his gentle features.

As he finally faced the door the noises became louder and clearer.

He cleared his voice "Captain Lev-"The words died on his tongue when he heard a very familiar voice let out a curse.

He tremblingly pressed his ear against the wall dreading the noises that were coming from the thin door.

"Levi fuck,your s-so tight"He heard Eren's voice hiss,that was all Armin needed to hear before bolting out of the hallway.

'Eren was supposed to be my alpha' Armin though sobbing,but then again they had mated but they still weren't mates.

"I was gonna ask Eren to be my alpha officially tomorrow" Armin whispered brokenly.

He shoved the files in Jean's arms leaving no explanation. He ran into his room and plopped face first into the top bunk bed.

"Armin are you okay?" Mikasa asked worriedly. He ignored Mikasa's frantic questions and fell into a deep slumber.

He woke up and grabbed breakfast without a word. "Hey Armin Mikasa told me you were crying,are you okay?"Asked Eren feigning worry.

"Why would you care?" Armin asked bitterly. "Well you are my boyfriend"Smirked Eren.

"I thought Levi was"He whispered brokenly. As if something snapped inside him Eren's eyes darkened before dragging Armin outside the lunch area.

"Armi-"He started but was cut off "What Eren,what"Interrupted Armin teary eyed.

"Armin the only reason we were dating was too get Levi jealous,I'm sorry Armin but Levi's a more capable Omega then you,I want Levi to be my mate"Said Eren firmly.

"Eren h-how could you do this"Asked Armin mortified that Eren could do something so horrible not remorseful.

"Armin can we do this another time,me and Levi were gonna meet up"Whispered Eren absent mindedly.

Pure hatred and loathing filled Armin and it visibly showed as Eren was backing up slowly,Armin grabbed Eren by his collar forcing him to meet his no longer teary eyed eyes.

"Why Eren,why did you choose me out of all the willing people why me"Armin asked determinedly.

"Well Levi would've been on to me if it wasn't anyone by you"responded Eren boredly.

"So why did you mate with me"Asked Armin a bold eyebrow raised at Eren honestly curious.

"Well so Levi would smell you on me,and that sex is sex"Eren shrugged.

Armin sneered at him "You're honestly disgusting"Sighed Armin dropping Eren.

As Armin left the room Eren was oddly turned on by this,Armin was usually timid and shy not like what he was acting like now,aggressive.

He sat down next to Marco confidently "Hello Marco"Armin greeted giving a nod in his direction.

"Hello..."said Marco suspiciously,"What's got you acting so different"Asked Marco curiously.

"Oh nothing"Said Armin sparing a glance at Eren.

"Eren why isn't Armin sitting over here"Asked Mikasa worriedly,"Oh we broke up"Said Eren sheepishly rubbing the nape of his neck.

"But I still don't understand why he's sitting with horse face"Said Eren irritated with a hint of jealousy.

"You broke up! Was it you?"Asked Mikasa accusingly,Eren raised his hands in defeat.

"He broke up with me,because of what I did"He whispered the last part," . "Asked Mikasa threateningly.

He told Mikasa everything from the start to the end,she blinked twice not comprehending what Eren was saying to her.

"Eren Armin was your best friend why'd you do that to him"Asked Mikasa twitching.

"I don't know Mikasa"Groaned Eren,"He should've understood"Muttered Eren.

"You were dating for a year and a half he should've killed you"Mikasa narrowed her eyes

"Whatever you'll notice the changes in your life without Armin"And without another word Mikasa left.

* * *

"Armin Can I come speak with you"Asked Levi gesturing to outside,Armin nodded his head dutifully.

"I know you're pregnant"Stated Levi bluntly,"So"Asked Armin crossing his arms.

Well the rules state pregnant Omegas or Betas can't fight"Levi stated simply.

"Okay"Said Armin boredly,"Okay?"Asked Levi confusedly. "I'm leaving when I start showing"Said Armin simply but firmly.

Levi walked off without another word.

* * *

Eren slowly but surely realized that Mikasa was right his life was becoming harder without Armin.

When he woke up in the morning he would want Levi beside him but Levi was embarrassed to be with Eren so he didn't tell anyone.

Armin however wasn't ashamed he loved Eren with all his heart,and looking back Eren regretted that he couldn't be more loving.

When he went to the lunch area he couldn't wrap his arms around Armin anymore.

He couldn't hear that cute laugh from Armin anymore.

His life was slowly but surely becoming hell.

Eren sighed looking at the gift Armin gave to him on their anniversary,it was something to numb his hand when he turned into a titan,it was a really thoughtful gift.

* * *

As Eren took his regular seat with Mikasa he noticed Reiner's arm wrapped around Armin's waist and him laughing joyfully.

He narrowed his eyes at the sight,unknowingly glaring at the two.

He watched wide eyed as Armin approached him "Hey Eren I forgive you,can we just forget the past year never happened"Asked Armin.

Eren nodded against his will not trusting his voice to speak.

"The reason I'm telling you this is that me and Reiner are leaving the Survey Corps"Armin explained.

Eren and Mikasa stood up"_What!?_" Eren and Mikasa shouted simultaneously,"I can't tell you the reason but it's for a good reason"Armin said conviction laced in his voice.

"Well this is goodbye I guess"Said Armin standing up to hug Mikasa tearfully and simply shaking Eren's hand.

Although a simple action,Eren's heart ached at Armin's farewell.

Armin and Reiner left the lunch area hand in hand after saying their farewells.

He decided that he couldn't take his heart aching any longer so he headed to Levi's room.

Eren walked into Levi's room without invitation,the sight he saw squeezed his heart even more.

Levi and Erwin were tangled in bed sweat and passion laced in the air.

"Levi"Eren whispered brokenly,"Yes Eren"Grunted Levi annoyed,"W-Why are you with Captain Erwin I-I'm supposed to be your alpha"Said Eren shaking with anger.

Levi laughed loudly "You think a whiny alpha like you who would leave a omega so quick to be with me I would make my mate"Levi deadpanned.

"W-why would you do this to me"Asked Eren,it hurt so much,he wondered why a decent human being would ever inflict it on another.

"Why'd you do it to Armin"Asked Levi cocking an eyebrow,he was silent "Exactly now get out,I'm spending time with my new alpha"Said Levi ushering him out.

Eren wanted to beat himself,is this what he did to Armin?.

He came to the slow realization that mating wasn't about power it was about love,and he loved Armin.

"Fuck"He cursed,he fucked up badly.

* * *

Eren entered Armin's room picking up random objects before stopping at Armin's journal.

He picked it up gently he opened the most recent page,the last one.

_Dear Journal today I will be leaving,I'm starting to show._

_Damn who would've thought that I would end up getting pregnant by Eren?_

_Well I'm not really in a relationship with Reiner._

_He's only coming with me so other alpha's won't try to claim me._

_Well Levi's going to dump Eren I know for sure._

_and frankly I don't care,an eye for an eye._

_Anyway I'm never gonna let Eren ever find out about the children._

_So this is the last time I'll ever write in this journal._

_I'll be traveling to the outside world Coronatia Cave is the specific location._

_Goodbye Journal._

Eren saw a few pages were wet probably from tears,Eren looked up determined.

He was going to Coronatia Cave.

* * *

**Authors Note:Well how was this chapter I'd like to say I did good since it's around 1'600 words so ya I'm proud of myself.  
**

**Anyway Favorite,Follow and review if you want me to continue.**

**Bye for now.**


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